1. Field of the Invention
The present invention pertains to surgical cutting instruments and, more particularly, to surgical cutting instruments having an elongated inner tubular cutting member rotating about its axis within an elongated outer tubular member having a cutting window at its distal end which cooperates with the inner member to cut, resect or abrade bodily tissue, the resulting loose tissue being aspirated through the lumen of the inner member.
2. Description of the Prior Art
The use of elongated surgical cutting instruments has become well accepted in performing closed surgery such as arthroscopic or, more generally, endoscopic surgery. In closed surgery, access to the surgical site is gained via one or more portals, and instruments used in the surgical procedure must be elongated to permit the distal ends of the instruments to reach the surgical site. Some conventional surgical cutting instruments (shavers) for use in closed surgery are rotary powered and have a straight, elongated outer tubular member and a straight, elongated inner tubular member concentrically disposed in the outer tubular member. The inner and outer members both separately and jointly are sometimes referred to in the art as "blades". The outer member has a distal end having an opening in the end or side wall (or both) to form a cutting port or window and the inner member has a distal end disposed adjacent the opening in the distal end of the outer member. The inner member is easily insertable into and removable from the outer member to facilitate cleaning or interchanging parts. Each of the elongated members has a hub or termination at its proximal end in order to attach the components to a rotary drive means. The distal end of the inner tubular member has a cutting means or cutting edge for engaging tissue via the opening in the distal end of the outer tubular member. In many cases (but not all) this distal cutting means cooperates with the opening in the outer member to shear, cut or trim tissue. In some cases, such as abrading burrs, the opening in the outer member merely allows access to the tissue and does not otherwise cooperate with the cutting means. The term "cutting edge" or "cutting means" as used herein is intended to include abrading (e.g. burrs) and other devices whether or not there is any traditional cutting or shaving action and whether or not there is any cooperative shearing action. The inner tubular member is rotatably driven about its axis from its proximal end, normally via a handpiece having a small electric motor which is controlled by either finger actuated switches on the handpiece, a foot switch or switches on a console supplying power to the handpiece. The distal end of the inner tubular member can have various configurations depending upon the surgical procedure to be performed, and the opening in the distal end of the outer tubular member would then have a configuration adapted to cooperate with the particular configuration of the distal end on the inner tubular member. For example, the inner and outer tubular members can be configured to produce whisker cutting, synovial resection, arthroplasty burring or abrading, side cutting, meniscus cutting, trimming, full radius resection, end cutting and the like, and the various configurations are referred to generically as cutting means. The loose tissue resulting from the cutting, resecting or abrading procedure is aspirated through the hollow lumen of the inner tubular member to be collected via a vacuum tube communicating with the handpiece.
The aforementioned elongated surgical cutting instruments have also been produced in angled configurations in which the axes of the distal tips of the inner and outer members are aligned and offset or bent at a fixed angle relative to the axes of the proximal ends of the aligned inner and outer members. Examples of such fixed-angle, rotary surgical instruments are shown in U.S. Pat. No. 4,646,738 (Trott), assigned to the assignee hereof, and in European Patent Application 0 445 918 (Krause et al.). In other respects the operation of these fixed-angle shavers is largely the same as that of the straight shavers described above. Known fixed-angle shavers are generally produced with only one offset angle--usually 15.degree.. Recently a variable-angle rotary shaver system has been introduced (described in a co-pending patent application assigned to the assignee hereof) in which the outer tube may be bent by a user to a user-selected angle while still enabling the inner tube to be selectively inserted into and removed from the outer tube. The angled shavers have a bend with a radius of curvature on the order of two to four inches. Tighter radii would be desirable.
In straight, fixed-angle and variable-angle prior art rotary shavers the inner tubular member has a proximal inner hub shaped to mate within an outer hub situated at the proximal end of the outer tubular member when the two members are assembled. The outer hub serves to lock the outer tubular member to the handpiece while the inner hub is adapted to mate with the motor drive shaft. Since most conventional rotary shavers utilize reusable handpieces with disposable shaver blades, the materials used to make the disposable blades must be cost-effective without adversely affecting performance. Consequently, the inner and outer hubs are generally molded plastic components while the bodies of the inner and outer tubular members are generally made of a biocompatible metal (generally 300 series stainless steel). The latter material is used in prior art inner tubular members because of the necessity to form sharp cutting means at the distal end of the inner member and because of the necessity to transmit a satisfactory amount of torque from the motor to the distal cutting means. The outer tubular member is made from metal in order to adequately hold the rotating inner member and resist any bending or kinking which would prevent rotation of the inner member.
In straight shaver configurations the elongated metallic tubular body of the inner member is generally integrally formed with the cutting means and the proximal end of the body is adhesively, thermally or ultrasonically bonded or otherwise affixed to the plastic hub. In the case of fixed-angle rotary shavers, however, a coupling device is interposed between the body and the cutting means. These prior art angled devices employ an outer member identical to that used in straight configurations (although angled to receive the bendable inner member) while the inner member is made from a metallic tubular body joined to the inner hub, a metallic distal cutting tip and some coupling means to join the two. In the aforementioned European patent application, for example, the coupling means is metallic and integrally formed with the body and tip, the coupling means being merely a portion of the inner member which is provided with relief apertures formed in the cylindrical surface to enable the inner member to bend as it rotates. In this embodiment, the metallic tubular body of the inner member is thermally bonded or otherwise affixed to the plastic hub as in the previously mentioned straight configuration.
Another fixed-angle shaver is known in which the tubular body of the inner member comprises a hollow metallic shaft affixed to the plastic hub, a metallic distal cutting tip and a coupling means formed of a plurality of counter-wound coiled metallic springs bonded to and interposed between the body and the tip. Such an embodiment is disclosed in the aforementioned U.S. Pat. No. 4,646,738 (Trott).
Another fixed-angle shaver is known in which the inner member has a plastic hub bonded to a metallic tubular body, a metallic distal tip and a coupling means formed of a single coil spring covered with a flexible plastic sleeve bonded to and interposed between the body and the tip.
The only known variable-angle shaver system has recently been introduced by Linvatec Corporation, 11311 Concept Boulevard, Largo, Fla. 34643 under the trademark MERLIN. This device incorporates a flexible inner member similar to that disclosed in the aforementioned U.S. Pat. No. 4,646,738 (Trott) and incorporates a unique, user-bendable outer tube.
One disadvantage of known coupling members is their inability to transmit sufficient torque at high rpm's through angles much greater than 15.degree.. As the benefits of angled shavers have been more and more widely appreciated, the angular limitation of prior art angled shavers has become a disadvantage to be overcome. It would, therefore, be advantageous to produce an angled rotary shaver capable of operation at angles greater than 15.degree..
In each known prior art system the requirement for adequate torque transmission along the inner member from the motor to the distal tip and the requirement for maintaining the sharpness of the cutting edge at the distal tip have been achieved by the use of metallic inner members formed almost entirely from biocompatible metallic materials such as stainless steel. The cost of obtaining and fabricating these materials into inner members is significant even though the combined inner and outer members are intended to be disposable. While the cost is significant even in the straight variety of shaver, the cost increases substantially in the fixed and variable-angle shavers because of the additional complexity involved in these devices. The coupling members of each of the known prior art angled rotary shavers are relatively complex when properly assembled to address the requirements of adequate torque transmission, sufficient lubricity to enable sustained operation at high rpm and sufficient sharpness. The number of component parts (springs, bearing sleeves, tubular bodies, cutting tips, etc.) and their assembly adds to the cost of these devices. It would be advantageous to produce both straight and angled rotatable shaver systems with fewer and/or less costly disposable components.
Another requirement imposed upon rotatable shavers is the necessity to maintain close tolerances between inner and outer members in order to maximize efficiency of operation. Obviously, such close tolerances must be balanced with the need to minimize friction to reduce heat and wear. This is generally done with the use of either lubricants or bearing surfaces--in either case adding to the cost of the device. In the case of angled shaver systems, the necessity to include bearing surfaces is even greater. Additionally, some angled shavers enable the inner member to bend within the outer tube by a configuration which often produces some gaps in the surface of the coupling means of the inner member resulting in a decrease of vacuum through the lumen of the inner member thereby compromising the ability of the device to aspirate tissue shavings through the lumen. This has been overcome in some instances by the use of a flexible polymeric sleeve situated over the bendable, coupling means portion of the inner member thus sealing any gaps while also providing a bearing function. The use of a solid cylindrical polymeric sleeve over a spring in some fixed-angle shavers may obviate the need for an encircling polymeric bearing sleeve. However, such bendable portions have less torque transmitting ability than other versions. The concern about maintaining close tolerances, adequate lubricity and vacuum sealing adds to the cost and complexity of prior art shavers and it would be advantageous to produce an inner member in which the disadvantages associated with these parameters could be minimized.
The rotatable inner members used in known angled shavers are either costlier than comparable straight, unbendable inner members or are not as efficient in transmitting torque. (Some prior art bendable inner members have torque transmission capability which is significantly--up to 50%--less than the straight counterpart.) This is most likely attributable to the coupling member. Nevertheless, this difference makes it necessary for manufacturers of these systems to produce both straight and bendable versions of inner tubular members--creating an undesirable inventory burden. It would, therefore, be advantageous to produce an elongated, rotatable tubular inner member which is less costly than conventional non-bendable inner members and which can be used either in a straight outer tubular member or in an angled outer tubular member without significant loss in its torque transmission ability.
Various embodiments of such elongated, rotatable tubular inner members are disclosed in co-pending application Ser. No. 08/058,504, assigned to the assignee hereof. One particular embodiment which has been found desirable utilizes a tubular member formed of polyetheretherketone (PEEK) which has a conventional plastic hub secured to its proximal end in a unique manner and a conventional metallic cutting tip secured to its distal end in a unique manner. The manufacture of a rotatable inner blade member having such a polymeric tube has been found to be facilitated by the invention disclosed herein and the operation and performance of such blades has been found to be enhanced.
Reliable and repeatable joining of a metallic cutting tip to a polymeric tube, particularly one made of PEEK, is difficult. Given the torsional forces to which the cutting tip is exposed, the junction between the tip and the tube must be preferably reinforced with some mechanical connection between the two elements if adhesive is to be used. However, certain mechanical junctions may weaken the wall of the inner tube so that the joint will fail at low torque values. If the design of the mechanical connection is strong enough, no adhesive or other bonding step is required other than merely pushing the tip onto the tube. Similarly, a mechanical connection may be designed for the proximal end of the tube at its connection to the hub. Such mechanical connections offer a significant advantage over the prior art which requires an adhesive or other bonding step to join the inner tube to the tip and the hub.
It is an object of this invention to produce an elongated rotatable inner tubular member for use in a rotatable shaver, the inner member having a non-metallic tubular body of a biocompatible polymeric or composite material that is mechanically joined to the cutting tip and/or hub of the inner member.
It is also an object of this invention to produce a method of producing a polymeric shaver blade member of a rotatable shaver blade, the method comprising steps for mechanically joining a cylindrical cutting tip to the tubular non-metallic inner member.
It is also an object of this invention to produce an elongated rotatable inner tubular member formed of PEEK that is mechanically joined to a cutting tip and/or hub.